Also an old article but worth a read:
How Costco Became the Anti-Wal-Mart

But not everyone is happy with Costco’s business strategy. Some Wall Street analysts assert that Mr. Sinegal is overly generous not only to Costco’s customers but to its workers as well.

Costco’s average pay, for example, is $17 an hour, 42 percent higher than its fiercest rival, Sam’s Club. And Costco’s health plan makes those at many other retailers look Scroogish. One analyst, Bill Dreher of Deutsche Bank, complained last year that at Costco “it’s better to be an employee or a customer than a shareholder.”

Mr. Sinegal begs to differ. He rejects Wall Street’s assumption that to succeed in discount retailing, companies must pay poorly and skimp on benefits, or must ratchet up prices to meet Wall Street’s profit demands.

Good wages and benefits are why Costco has extremely low rates of turnover and theft by employees, he said. And Costco’s customers, who are more affluent than other warehouse store shoppers, stay loyal because they like that low prices do not come at the workers’ expense. “This is not altruistic,” he said. “This is good business.”